1. Field of the Invention
The present invention relates to an apparatus for processing of semiconductor wafers and the like, and more particularly, to a reactor having rotating components to produce a more uniform deposition.
2. Description of the Related Art
High-temperature ovens, called reactors, are used to create structures of very fine dimensions, such as integrated circuits on semiconductor substrates. One or more substrates, such as silicon wafers, are placed on a wafer support inside the reaction chamber. Both the wafer and support are heated to a desired temperature. In a typical wafer treatment step, reactant gases are passed over the heated wafer, causing the chemical vapor deposition (CVD) of a thin layer of the reactant material on the wafer. If the deposited layer has the same crystallographic structure as the underlying silicon wafer, it is called an epitaxial layer. This is also sometimes called a monocrystalline layer because it has only one crystal structure. Through subsequent processes, these layers are made into integrated circuits, producing from tens to thousands or even millions of integrated devices, depending on the size of the wafer and the complexity of the circuits.
Various process parameters must be carefully controlled to ensure the high quality of the resulting layers. One such critical parameter is the temperature of the wafer during each treatment step of the processing. During CVD, for example, the deposition gases react at particular temperatures and deposit on the wafer. If the temperature varies across the surface of the wafer, uneven deposition of the reactant gas occurs and the thickness and resistivity will not be uniform. Non-uniformity of deposited layers also results from an uneven distribution of reactant gases over a wafer. Accordingly, it is important that wafer temperature and gas distribution be stable and uniform across the wafer.
Similarly, non-uniformity or instability of temperature across a wafer during other thermal treatments can affect the uniformity of resulting structures. Other processes for which temperature control can be critical include oxidation, nitridation, dopant diffusion, sputter depositions, photolithography, dry etching, plasma processes, and high temperature anneals.
One way that reactors have attempted to overcome the aforementioned problems is to provide a rotating wafer. An example of one such reactor is shown in U.S. Pat. No. 4,821,674. This reactor includes a circular rotatable susceptor having a diameter slightly larger than the wafer. The rotatable susceptor rotates the wafer about an axis normal to the center of the wafer. Rotation of the susceptor causes an averaging of the deposited material growth rates, alleviating the problem of concentration depletion of deposition materials as the reactant gas flows past the substrate. Rotation of the susceptor also produces an averaging of the temperature gradient, which results in a reduction in the temperature differences both in the susceptor and in the substrate being supported thereon.
Attempts to improve uniformity of deposition have also been made by providing a reactor with a showerhead gas inlet, as described in U.S. Pat. No. 4,798,165. In this reactor, gas is directed to a substrate through a plurality of apertures in a showerhead configuration to cause uniform gas flow over the surface of the substrate. Non-uniformity of deposition can further be reduced in this reactor by rotating the substrate as reactant gas showers down on the wafer.
Despite the advances in temperature and gas distribution uniformity in the reactors described above, a need still exists for a reactor or semiconductor processing apparatus that further improves uniformity of deposition. Accordingly, it is an object of this invention to provide a reactor or semiconductor processing apparatus that overcomes the limitations of the prior art to provide better temperature uniformity and gas distribution uniformity.